Markets are falling because going over the cliff creates uncertainty. The uncertainty revolves around not just not paying the interest but also other factors such as a downgrade by the ratings agencies and the impact on growth. Treasuries are the lynchpin of the global financial system. Anything that threatens the sanctity of Treasuries damages the financial markets and the economy. Your contention that the market has already discounted the uncertainty is sheer nonsense.
All those catastrophic possibilities, and the market downturn isn't even a correction yet. Which is why I said you don't know asset valuation. You also said the market would react after the event.
I've known a lot of mediocrities in The City who had impressive titles and job descriptions and didn't have a clue what was going on around them.